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- Nếu \(a=c=0\Rightarrow\left(\frac{a-b}{c-d}\right)^{2019}=\left(\frac{b}{d}\right)^{2019}=\frac{b^{2019}}{d^{2019}}\)
\(\frac{2a^{2019}-b^{2019}}{2c^{2019}-d^{2019}}=\frac{-b^{2019}}{-d^{2019}}=\frac{b^{2019}}{d^{2019}}\Rightarrow\left(\frac{a-b}{c-d}\right)^{2019}=\frac{2a^{2019}-b^{2019}}{2c^{2019}-d^{2019}}\)
- Nếu \(a;c\ne0\)
\(\frac{a}{b}=\frac{c}{d}\Rightarrow\frac{a}{c}=\frac{b}{d}=\frac{a-b}{c-d}\)
\(\Rightarrow\frac{2a^{2019}}{2c^{2019}}=\frac{a^{2019}}{c^{2019}}=\frac{b^{2019}}{d^{2019}}=\left(\frac{a-c}{b-d}\right)^{2019}=\frac{2a^{2019}-b^{2019}}{2c^{2019}-d^{2019}}\)
Này Nguyễn Việt Lâm, mk thấy cái trường hợp a;c\(\ne\)0 nó cứ làm sao sao ấy.Bn thử kiểm tra lại xem
Đặt \(\frac{a}{b}=\frac{c}{d}=k\)
\(\Rightarrow\hept{\begin{cases}a=bk\\c=dk\end{cases}}\)
\(\frac{a^{2019}+c^{2019}}{b^{2019}+d^{2019}}=\frac{\left(bk\right)^{2019}+\left(dk\right)^{2019}}{b^{2019}+d^{2019}}=\frac{b^{2019}.k^{2019}+d^{2019}.k^{2019}}{b^{2019}+d^{2019}}=\frac{k^{2019}.\left(b^{2019}+d^{2019}\right)}{b^{2019}+d^{2019}}=k^{2019}\)(1)
\(\frac{\left(a+c\right)^{2019}}{\left(b+d\right)^{2019}}=\frac{\left(bk+dk\right)^{2019}}{\left(b+d\right)^{2019}}=\frac{[k.\left(b+d\right)]^{2019}}{\left(b+d\right)^{2019}}=\frac{k^{2019}.\left(b+d\right)^{2019}}{\left(b+d\right)^{2019}}=k^{2019}\)(2)
Từ (1) và (2) \(\Rightarrow\frac{a^{2019}+c^{2019}}{b^{2019}+d^{2019}}=\frac{\left(a+c\right)^{2019}}{\left(b+d\right)^{2019}}\)
Mình viết sai đề đó nha
Bài giải
* Từ \(\frac{a}{b}=\frac{c}{d}\text{ }\Rightarrow\text{ }\frac{a}{c}=\frac{b}{d}\text{ }\Rightarrow\text{ }\frac{a^{2019}}{c^{2019}}=\frac{b^{2019}}{d^{2019}}=\frac{a^{2019}+b^{2019}}{c^{2019}+d^{2019}}\text{ ( * ) }\)
* Từ \(\frac{a}{c}=\frac{b}{d}=\frac{a-b}{c-d}\text{ }\Rightarrow\text{ }\frac{a^{2019}}{c^{2019}}=\frac{\left(a-b\right)^{2019}}{\left(c-d\right)^{2019}}\left(\text{**}\right)\)
* Từ \(\left(\text{*}\right),\left(\text{**}\right)\Rightarrow\text{ ĐPCM}\)
